Rotational relaxation of solute molecules in dense noble gases and the relation with local anisotropy fluctuations

Abstract

Many molecular relaxation processes in fluids are sensitive to the time-dependence of local, anisotropic density fluctuations. The role played by anisotropic density fluctuations in the rotational relaxation of a linear, quantized rotor will be discussed in some detail. An expression for the dipolecorrelation function of a probe molecule, dissolved in a simple fluid, will be derived along these lines. This expression will be shown to account for the experimentally observed density-dependence of the rotational linewidths of HCl in argon. Some simple models for anisotropic density fluctuations or, more precisely, for the four-point density-correlation functions, will be discussed.